Not enough freebore ?

[Dave in WI]

Customer brought in a rifle that was built somewhere else. Chambered in 6.5 PRC. When chambering factory Hornady 147ELD it grabs the bullet out of unfired round and pull it out when tried to extract it. I split the neck of a case and put the factory bullet in there to check for bullet seating depth in this chamber. Using that method, my bullet comes out .060 inches shorter than the factory loaded rounds. Here are some pictures of the freebore. Looks like the lands come almost all the way to the neck.

 

[Jud96]

I’ve seen this exact thing happen in a 6.5 PRC with factory ammo.

The SAAMI reamer dimensions in the freebore are .2645 and the Hornady bullets I measured were .2643-.2644 in the particular box the customer was using. If the reamer is worn in the freebore area just a little bit it will cause it to be tight.

The fix was running a sharp reamer in the chamber to just clean up the throat. You could also use a throating reamer to do the same thing.

 

[Dave in WI]

Thank you. Pic of bullet that was chambered

 

[SKWERLZ]

It’s throating reamer time.

 

[Dave in WI]

It's about time I learn to use a uni-throater. I'll order one out.
Thanks, guys.

 

[Jud96]

Thank you. Pic of bullet that was chambered
View attachment 1761916

Yep you can see where it’s rubbing the freebore. If it was in the lands it would just have the marks from each individual land.

You can mic the bullet and see what it actually measures.

 

[LVLAaron]

This is why when I was spec'ing my first custom reamer, everyone told me go a full thou over bullet diameter.

 

[Dave in WI]

Bullets are measuring .2644"

 

[Jud96]

Tight freebore spec, probably a worn reamer, and fat bullets is a recipe for problems

As @LVLAaron mentioned, I also have been advised and spec my reamers .0007-.001 over nominal bullet diameter. The reamer manufacturers have a plus tolerance so you know you’ll at least be right on size which will give you clearance even on a fat lot of bullets.

 

[SKWERLZ]

This is why when I was spec'ing my first custom reamer, everyone told me go a full thou over bullet diameter.

^^^^

 

[LVLAaron]

Tight freebore spec, probably a worn reamer, and fat bullets is a recipe for problems

As @LVLAaron mentioned, I also have been advised and spec my reamers .0007-.001 over nominal bullet diameter. The reamer manufacturers have a plus tolerance so you know you’ll at least be right on size which will give you clearance even on a fat lot of bullets.

Plus a little bit of carbon ring during a 60 shot match... things go south real easily.

 

[SKWERLZ]

It's about time I learn to use a uni-throater. I'll order one out.
Thanks, guys.

The fancy one PTG makes is a no brainer, super easy to get good results and control depth.

The simpler ones aren’t bad.

 

[Dave in WI]

The fancy one PTG makes is a no brainer, super easy to get good results and control depth.

The simpler ones aren’t bad.

I ordered the PTG one.

 

[LVLAaron]

I ordered the PTG one.

They're like a hot knife through butter. Proceed carefully.

 

[jackieschmidt]

They're like a hot knife through butter. Proceed carefully.Very Carefully.

^^^^^^^
Very Carefully.

 

[ELR LVR]

^^^^^^^
Very Carefully.

Yes you wont even feel it cutting
Be sure to use some sort of stop to not go too deep
---
And a helpful tip, make a centering tool to keep it centered within the bore
IE: dont just use your tailstock and a live center on the rear

 

[LVLAaron]

^^^^^^^
Very Carefully.

Good friend of mine brought a panda barrel over and a seated round. Easy job, set this back a thread and throat it for this round plus 10 thou. No problem. I set it up, barrel in the lathe, major work done, just need to throat it a little bit.

I run the throater a few thou. Test fit the dummy round. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat..... Repeat.

OK something is wrong.


Long story short... The piece of brass had been fired several times and wouldn't seat in the chamber so I kept going with the throater. Measured it. Pulled it apart. Sized the brass. re-seated, and started over, with the barrel an inch shorter.


I follow this unrelated tradesman who always says "If you aren't testin you're guessin". It applied here...Something I've been saying a lot lately to my team is "Most valuable lessons are either expensive or painful"

 

[ELR LVR]

Good friend of mine brought a panda barrel over and a seated round. Easy job, set this back a thread and throat it for this round plus 10 thou. No problem. I set it up, barrel in the lathe, major work done, just need to throat it a little bit.

I run the throater a few thou. Test fit the dummy round. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat..... Repeat.

OK something is wrong.


Long story short... The piece of brass had been fired several times and wouldn't seat in the chamber so I kept going with the throater. Measured it. Pulled it apart. Sized the brass. re-seated, and started over, with the barrel an inch shorter.


I follow this unrelated tradesman who always says "If you aren't testin you're guessin". It applied here...Something I've been saying a lot lately to my team is "Most valuable lessons are either expensive or painful"

This is a mistake I'm sure some of us have made, I've done it once too
And kicked myself assuming all things were correct because the Case being FL sized all the way is just something we assume would be right. Especially when it holds a bullet tight lol
Having a bullet seated in a dummy round as a gauge for throat depth where we want it and test by closing the bolt on the dummy round
if it wont close or we feel resistance, we assume it is the bullet hitting the lands, so of course throat deeper until the bolt will close on dummy round
Only way to be sure - is to FL size a case yourself - as opposed to someone else doing so
(Some people provide their own dummy round but it may not be sized all the way)
Test that the bolt closes easily on the FL sized case before making your dummy round with that case
---
Another way to check to help prevent this or even gauge a starting point
is the same method I use to gauge bullet hitting the lands
Insert bullet into chamber and lightly tap it into place into the lands
come in from the muzzle with a cleaning rod and touch the meplat of the bullet
and mark the rod at the end of the muzzle, this will show where the lands actually stop the bullet.
Will also show OAL for making a dummy round
---
Then as one throats, you can keep using that bullet barely tapped into the lands
and gauge depth with a cleaning rod